What is this otter eating?

What is this otter eating?

Observation - What is this otter eating? - UK and Ireland. Description: At the end of July, we watched an otter for over an hour in the early evening on the river near the centre of Thetford. It spent most of its time diving and foraging among some quite dense patches of vegetation, often emerging with something and then chew

At the end of July, we watched an otter for over an hour in the early evening on the river near the centre of Thetford. It spent most of its time diving and foraging among some quite dense patches of vegetation, often emerging with something and then chewing it before diving again. The otter was very close at times - sometimes as little as 2 metres! - and I got several good views of what it was eating - about the same size and colour as a small conker, but with a rather gelatinous appearance. I have been in touch with a couple of otter charities, but neither has been able to offer a convincing explanation of what the food might be. I've had lots of suggestions but can anyone offer a definitive identification?